Accuracy of shear properties of wood obtained by simplified Iosipescu shear test

We examined the accuracy of the shear properties of wood by the Iosipescu shear test using specimens whose shape was simplified. Quartersawn boards of sitka spruce (Picea sitchensis Carr.) and shioji (Japanese ash,Fraxinus spaethiana Lingelsh.) were used. Two types of specimen for the Iosipescu shear test were compared: a standard specimen whose notch angle is 90° and a keyhole type specimen, which is more easily prepared than the standard type. The shear modulus, yield shear stress, and failure shear stress of the keyhole-type specimen were compared to those of the standard specimen. Shear stress analysis was conducted using the finite element method (FEM). The results obtained were as follows: (1) The failure pattern obtained by the simplified Iosipescu shear test was similar to that seen with the standard Iosipescu shear test. (2) The shear modulus, yield stress, and failure stress obtained by the simplified Iosipescu shear test coincided with those by the standard Iosipescu shear test. (3) The principal strain angle and principal stress angle of the simplified Iosipescu shear test were about 45°. (4) It is recognized that pure stress is applied to the strain-gauge regions in the simplified Iosipescu shear test, and it is expected that the shear properties are independent of the notch angle.     

Applicability of the losipescu shear test on the measurement of the shear properties of wood

We examined the applicability of the Iosipescu shear test for measuring the shear properties of wood. Quarter-sawn board of sitka spruce (Picea sitchensis Carr.) and shioji (Japanese ash,Fraxinus spaethiana Lingelsh. were used for the specimens. Iosipescu shear tests were conducted with two types of specimen whose longitudinal and radial directions coincided with the loading direction. The shear modulus, yield shear stress, and shear strength were obtained and were compared with those obtained by the torsion tests of rectangular bars. The results are summarized as follows: (1) The Iosipescu shear test is effective in measuring the shear modulus and the yield shear stress. (2) To measure the shear strength properly by the Iosipescu shear test, the configuration of specimen and the supporting condition should be examined in more in detail.     

Evaluation of a modified Iosipescu shear test method for determining the shear properties of clear wood

A modified Iosipescu shear test method is proposed as an alternative for measuring the shear properties of clear wood. The method adopts four-point asymmetric loading procedure in the Iosipescu shear test but with the loading positions shifted to the neutral axis of the specimen. The original V-notched specimen is replaced by a combination of polyvinyl chloride blocks at two ends and a bow-tie-shaped wood specimen in the middle to provide a better stress pattern at failure. The measured shear strength and shear moduli are compared with results from compression test and off-axis tension test. Finite element analysis is also carried out to study the stress distribution in the wood specimen. Results show that the new shear test setup can provide close-to pure shear stress state in the specimen yielding better estimates of the shear properties of wood. The shear strength obtained by the new test setup is slightly lower than that from the off-axis tensile test which is probably due to the relatively thick specimen chosen in this study.     

云杉胶合木钢板斜螺钉连接的剪切性能研究

为准确评价斜螺钉连接钢 木节点的剪切性能,探明其受力机理,以云杉胶合木、钢板和自攻螺钉作为研究材料,测试不同荷载方向与受力情况下斜螺钉连接节点的承载性能,将试验数据与国外规范中的计算模型进行对比,提高了侧边钢板 胶合木(钢 木)斜螺钉连接节点承载性能的预测能力。结果表明:自攻螺钉与剪切面之间的角度变化对其在钢 木节点承受剪 压复合应力的承载力影响不明显,当偏转为剪 拉复合应力时,节点承载力明显增大,并在30°~45°获得最大值;剪 压复合应力时,现行EC5公式计算剪 压节点的极限承载力非常不安全;EC5的刚度预测结果在剪 压复合应力区和垂直剪切面钉入时,与试验值吻合度很高,但对剪 拉区节点的滑移模量没有预测性;将Tomasi模型应用于斜螺钉连接钢 木节点滑移模量理论计算时,在45°~90°时与试验值吻合度极高。单颗自攻螺钉的抗拔刚度计算节点滑移模量的方法极为有效,具有较高的借鉴意义。     

定向刨花板剪切模量和弹性模量动态测试

【目的】研究定向刨花板(OSB)的各向异性,探讨OSB面内剪切模量动态和静态测试方法,以提供一种快速、简便、重复性好、精度高的动态测试方法测量和分析OSB弹性常数。【方法】应用ANSYS程序计算OSB自由板和悬臂板试件的振形系数,给出振形系数依赖于板长宽比和宽厚比的关系式,通过仿真计算、动态试验和方板静态扭转试验验证其正确性。动态试验测试OSB剪切模量试件从一块整张OSB上下料制作,分为3个方向,即沿整板纵向下料制作的试件(0°或x向)、横向方向下料制作的试件(90°或y向)和沿与纵向呈45°方向下料制作的试件;方板扭转试验测试OSB剪切模量试件沿整板纵向或横向下料制作;动态测试OSB纵向、横向和45°方向弹性模量以及面内剪切模量和45°方向剪切模量。【结果】OSB实测纵向弹性模量是横向弹性模量的2.89倍,45°方向剪切模量小于面内剪切模量。正交各向异性材料方板扭转试验测试剪切模量推算公式需用±45°方向应变测量值的差值进行推算,将其用于OSB,测得的静态剪切模量与动态测试的剪切模量相当吻合。【结论】OSB弹性模量具有方向性,纵向最大,横向最小,45°方向介于二者之间;自由板扭转振形法和悬臂板扭转模态法适用于动态测试OSB面内剪切模量,其正确性得到方板扭转试验验证;0°和90°OSB动态测得的剪切模量几乎相等,可作为OSB面内剪切模量Gxy的估计值;OSB不宜按单向复合材料处理,在理论分析时宜按正交各向异性处理,OSB45°方向的剪切模量G45°相似文献   

Estimation of the shear strength of wood by uniaxial-tension tests of off-axis specimens

To determine shear strength we conducted uniaxial-tension tests of off-axis specimens and examined the proper off-axis angles. Sitka spruce (Picea sitchensis Carr.) and katsura (Cercidiphyllum japonicum Sieb. and Zucc.) were used for the studies. Uniaxial tension tests of the specimens with various off-axis angles were conducted, and the shear stress at failure was obtained. Independent of the tension tests, torsion tests were conducted, and the shear strengths were obtained. Comparing the data of the uniaxial tension and torsion tests, we examined the validity of estimating shear strength by the off-axis tension test. The shear strengths obtained from the tension tests coincided well with those measured by the torsion tests when the specimen had an off-axis angle of 15°–30°. In this off-axis angle range, the tensile stress perpendicular to the grain might have a serious influence on the shear strength, and we thought that the shear strength predicted by uniaxial tension tests should be treated as an approximate value despite the simplicity of the tension test. Other test methods should be adopted to obtain the precise shear strength of wood.     

Measurement of the shear modulus of wood by static bending tests

When measuring the shear modulus of wood by static bending tests, the basic theory is dependent on Timoshenko's bending theory. The shear modulus obtained by static bending is a much smaller value than that derived by other methods. We examined the applicability of Timoshenko's theory and propose an empirical equation that can derive the shear modulus properly. Three softwoods and three hardwoods were used for the tests. First, the Young's modulus and shear modulus were measured by free-free flexural vibration tests. Then the three-point static bending tests were undertaken, varying the depth/span ratios. Additionally, the bending tests were simulated by the finite element method (FEM). The shear moduli obtained by these methods were then compared. The deflection behaviors in static bending were not expressed by the original Timoshenko bending theory because of the stress distortion near the loading point. Based on the experimental results and numerical calculations, we modified the original Timoshenko bending equation. When using our modified equation the stress concentration must be carefully taken into account.     

Effect of element type on the internal bond quality of wood-based panels determined by three methods

Three mechanical tests with different loading modes were conducted to evaluate the effect of element type on the internal bond quality of wood-based panels. In addition to the internal bond test, which is commonly used for mat-formed panels, interlaminar and edgewise shear tests were used to test oriented strandboard (OSB), particleboard, medium-density fiberboard (MDF) of two thicknesses, and plywood. The following results were obtained. Epoxy resin proved to be suitable for determining the interlaminar shear modulus instead of hot-melt glue. There was a linear relation between panel density and interlaminar shear modulus and a linear correlation between the interlaminar shear strength and internal bond (IB) strength for the mat-formed panels tested. OSB had the highest edgewise shear modulus, and MDFs had the highest edgewise shear strength in this study. The modulus/strength ratio also depended on both panel type and loading mode. The relation between the shear moduli determined from the edgewise and interlaminar tests indicated the characteristics of the shear properties of panels made of different elements.Part of this paper was presented at the Fourth International Wood Science Symposium, Serpong, Indonesia, September 2002     

Combined shear and compression analysis using the Iosipescu device: analytical and experimental studies of medium density fiberboard

The possibility of using the Iosipescu shear test device to study the combined shear and compression behavior of anisotropic materials was examined. Measurements were made using both an original (Wyoming version) and an in-house modified Iosipescu shear and compression fixture. Numerical simulation of the combined shear and compression test was carried out to verify the reliability of the modified device. The numerical results were compared with data from experiments on a medium-density fiberboard. The numerical results show good agreement with the experimental results for the shear test in all the three material directions tested. The shapes as well as the values of the strain fields were similar in the numerical and experimental results. Different rotations of the combined shear and compression device were studied using the finite element method to find the combinations that gave reliable results in shear and compression. It was found that the 45° rotation gave the most uniform strain fields in the section between the notches. This rotation was tested on the fiberboard.     

Measurement of the shear modulus of wood by asymmetric four-point bending tests

We conducted asymmetric four-point bending tests of wood and obtained the shear moduli on the basis of Timoshenko's theory of bending. Akamatsu (Japanese red pine,Pinus densiflora D. Don) and shioji (Japanese ash,Fraxinus spaethiana Lingelsh.) were used for the tests. Asymmetric four-point bending tests were undertaken by varying the depth/span ratios; and Young's modulus and the shear modulus were calculated by Timoshenko's bending theory. Independent of the asymmetric bending tests, we also conducted three-point bending tests, free-freeflexural vibration tests, and numerical calculations by the finite element method. Young's and shear moduli obtained by these methods were compared with those derived from the asymmetric bending tests. Based on these comparisons, we concluded that the shear modulus can be properly obtained by the asymmetric four-point bending tests when the span is 20 times larger than the depth.     

Estimation of the internal shear strength distribution of the element for laminated veneer lumber by nonlinear least-squares method

Until now we developed an estimation method for strength distributions of laminated veneer lumber (LVL) element by nonlinear least-squares method (NLM). Estimated strengths by this method were modulus of elasticity (MOE) and modulus of rupture (MOR) in the horizontal use direction and the vertical use direction, tensile strength and compression strength. But to use LVL for structural members, shear strength was also needed. Therefore, we tried to estimate the shear strength distribution of LVL element by NLM same as MOE and MOR in the horizontal use direction and the vertical use direction, the tensile strength of LVL and the compression strength of LVL in the previous reports. We conducted shear strength test for LVL and estimated element shear strength distribution by LVL strength data in the horizontal and vertical use direction. Next, we simulated LVL shear strength distribution using element shear strength distribution and compared with experimental ones in each use direction. They were overlapped in both use direction. Therefore, we could validate NLM for estimating element shear strength distribution.     

Measurement of bending properties of wood by compression bending tests

We measured Young's modulus, proportional limit stress, and bending strength by the compression bending test and examined the applicability of the testing method by comparing it with conventional bending test methods. Long columns of todomatsu (Japanese fir,Abies sachalinensis Fr. Schmidt) with various length/thickness ratios were the specimens. A compressive load was axially applied to the specimen supported with pin ends. Young's modulus, the proportional limit stress, and the bending strength were obtained from the load-loading point displacement and load-strains at the outer surfaces until the occurrence of bending failure. Four-point bending tests were also conducted, and the bending properties obtained were compared with the corresponding properties obtained by the compression bending tests. Based on the experimental results, we believe that when the stress-strain relation is measured by the load-loading point displacement relation using specimens whose length/thickness ratio is large enough, the bending properties can be obtained properly using the compression bending test.     

Vibrational properties of wood plastic plywood

Wood plastic plywood (WPPW), composed of veneer and styrofoam, was manufactured without special adhesives such as urea–formaldehyde or phenol–formaldehyde resins, and its vibrational properties were investigated. WPPW can be produced at 1MPa and 160°C for 9min (three-ply) and 12min (five-ply). The dynamic Youngs modulus reached its highest value when the styrofoam thickness was 30mm. The sound velocity and dynamic Youngs modulus had minimum values at a grain angle of 45°. The results for dynamic Youngs moduli measured by a longitudinal vibration method and an in-plane flexural vibration method were almost the same. Dynamic shear moduli were measured by an in-plane surface wave propagation test and an in-plane flexural vibration method. From the experimental results, the dynamic shear moduli at 0° and 90° by the two methods were relatively close, although the surface wave propagation test results were higher than those from the flexural vibration method. Dynamic shear moduli at a grain angle of 45° measured by the in-plane surface wave propagation test and calculated from theory were relatively close. The surface wave propagation test results were smaller than the results calculated from theory. The shear stress distribution factors were about 1.000–1.189 for WPPW.     

Bending and shear properties of compressed Sitka spruce

We examined the bending and shear properties of compressed wood using small and clear specimens of Sitka spruce (Picea sitchensis Carr.). For measuring the bending properties, three-point bending tests were conducted under the span/depth ratio of 14, which is standardized in the American Society for Testing and Materials [ASTM D143-94 (2005a)] and Japanese Industrial Standards [JIS Z2101-94 (1994)]. In the bending test, the load, deflection at the midspan, and strain at the bottom of the midspan were simultaneously measured, and Young’s modulus and bending strength were obtained by elementary beam theory. For obtaining the shear modulus and shear strength, asymmetric four-point bending tests were conducted using the specimens with rectangular and side-grooved cross sections, respectively, and the influence of the compression ratio on the shear properties was examined. The results are summarized as follows: (1) Young’s modulus increased with increasing compression ratio when it was determined by the load–strain relation. Nevertheless, this tendency was rather obscured when Young’s modulus was determined by the load–deflection relation. Hence, it is preferable that Young’s modulus is measured from the load–strain relation. (2) The shear modulus in the longitudinal–tangential plane was maximum at the compression ratio of 50%, whereas that in the longitudinal–radial plane was minimum at the compression ratio of 50%. (3) The influence of the compression on the bending and shear strength ratio was not significant.     

Estimation of shear moduli of wood by quasi-simple shear tests

A quasi-simple shear test, which is the most direct method for examining the shear properties of sheet metals, has been applied to measure the shear moduli of wood. Buna (Fagus crenata Blume) with variously sized shear regions was used for the test specimens. Strain gauges were mounted in the center of the shear regions to measure the shear strains. The shear tests were carried out to determine the shear moduli in the radial and tangential planes. Apparent shear moduli obtained from the experimental results were corrected by finite element method (FEM) simulation of the shear region, where both shearing and bending are produced. It was found that the corrected shear moduli are roughly independent of test conditions, and their values are in good agreement with the data obtained from bending-shear tests. This suggests that the method employed here can effectively estimate the shear moduli of wood.Part of this research was presented at the 50th Annual Meeting of the Society of Materials Science, Osaka, May 2001     

Development of an air-injection press for preventing blowout of particleboard IV: effects of air-injection conditions on board performance and formaldehyde emission

An air-injection press, which has holes punched in the heating plates, injects high-pressure air through the holes of one plate into particleboard and discharges the air through the other plate during press heating. The press can manufacture particleboard from high-moisture particles by controlling blowout of the boards. In this study, the optimum diameter and spacing of the air-injection holes and the effects of pre- and post-pressing were investigated. An optimum hole diameter was not found for the modulus of rupture and thickness swelling for a spacing of either 25 or 50 mm. In terms of internal bond strength, the optimum diameter of the holes arranged at a spacing of 25 mm was 1 mm, but the internal bond strength was not changed by the diameter of holes spaced 50 mm apart. Air injection under all hole conditions reduced the formaldehyde emission from the board. Pre-pressing was tested for further increase in the modulus of rupture and internal bond strength, but was found to have no effect. More efficient use of the air-injection press was achieved by injecting air from the early stages of pressing.     

仿生木材结构穿孔纤维板吸声性能

以中密度纤维板为基材,通过设计穿孔结构及打孔方式,达到拓宽木质穿孔板吸声频带和提高声学性能的目的.利用分层加工工艺制备了带侧孔结构的穿孔纤维板,采用阻抗管传递函数法对穿孔纤维板吸声性能进行了测试.通过正交试验方法,研究了主孔直径、穿孔率、倾斜角度对穿孔纤维板吸声性能的影响,并获得了较优的制备工艺,随后利用控制变量法研究...     

Evaluation of quality indexes of bending performance and hardness for hardwoods

The mechanical properties of 613 small clear specimens of 35 species (11 ring-porous hardwoods, 19 diffuse-porous hardwoods, and 5 softwoods) were evaluated. The aim of the study was to examine indexes of wood quality that are easy to measure and that exhibit a high correlation with bending performance and hardness that are essential properties of hardwood products. The modulus of rigidity, dynamic modulus of elasticity, bending properties (modulus of elasticity, modulus of rupture, stress at the proportional limit, absorbed energy, Tetmajer’s modulus), dynamic energy absorption by an impact bending test, compressive strength parallel to the grain, shear strength, partial bearing strength, and Brinell’s hardness were measured. A high correlation was found between dynamic modulus of elasticity and static modulus of elasticity. Bending stress at the proportional limit was found to be approximately equivalent to the compressive strength parallel to the grain. Static energy absorption correlated with dynamic energy absorption. Tetmajer’s modulus was found to be closely related to the ratio of the initial stiffness within the elastic range to the secant modulus at the maximum load. A high correlation was observed between Brinell’s hardness and partial bearing strength. The difference in the regression coefficients obtained for these correlations between the species groups was small. Part of this study was presented at the All Division 5 Conference of IUFRO, Taipei, October 2007     

Utilization of digital image correlation in determining of both longitudinal shear moduli of wood at single torsion test

A sophisticated approach for the precise determination of both longitudinal shear moduli of wood at single test is introduced. The method is based on the combination of the torsion test inducing pure shear stresses in sample and an optical method providing the full-field strain data of such stress state. The proposed procedure of the longitudinal shear moduli determination consists of two main steps. In the first step, the apparent longitudinal shear modulus following the standardized procedure (EN 408+A1) was determined. Secondly, both longitudinal shear moduli were derived based on the apparent longitudinal shear modulus and the shear strain distribution on the radial and tangential sample surfaces. The wood of European beech (Fagus sylvatica L.) was used as material for the experiments. The exploratory analysis revealed the increasing difference between the longitudinal shear moduli determined in the longitudinal–radial plane and in the longitudinal–tangential plane as the total torsion angle increased as well as with the increase in the average torsion stiffness. Further, the longitudinal shear moduli and the torsional longitudinal shear strength did not correlate well. Therefore, they cannot be used in order to predict each other. Although such findings need more detailed studies, they should be taken into account when designing wood structures.     

木榫旋转焊接节点剪切试验研究与理论分析

为研究无胶层合木梁中旋转焊接木榫的抗剪性能,选用山毛榉木榫旋转焊接SPF(spruce-pine-fir)层板,制备20个单榫焊接节点试件开展双剪试验,获得其破坏模式及荷载-位移曲线.试件的破坏模式为木榫受剪出现类双铰破坏,同时开孔附近基材受木榫挤压破坏.试件的平均峰值位移为4.460 mm,平均峰值荷载为6.127 ...